The invention relates to a head end for a signal distribution system, comprising a space division switching network for selectively switching wide-band input signals to a plurality of outputs, to which a multiplexing arrangement is connected for forming at an output thereof a composite signal which is thereafter used for the signal distribution.
The invention also relates to a receiver suitable for processing the composite signal generated by the head-end of the distribution system, the receiver comprising a demultiplexing arrangement for deriving at least one wide-band signal from the composite signal.
Such a head-end and such a receiver for a signal distribution system are inter alia used in combination with light transmission through optical fibres. The signal-to-noise ratio of an optical transmission path is such that in practice, it is usually preferable to use digital modulation methods having a small number of modulating levels. In addition, in the space division switching network (matrix), cross-talk occurs between the different signals. This cross-talk can be counteracted by reclocking the digital signal streams after switching by the matrix. This, however, can only be achieved in a simple way with mutually synchronous digital signal streams.
Mutually synchronous digital signal streams can be time-division mutliplexed, as a result of which a digital signal stream having a high bit rate is produced. In practice, this bit rate may easily exceed the capacity of the transmission channel for the transmission of television video signals. Thus, the bandwidth - distance characteristic number for a graded-index fibre is at present approximately 700 MHz.Km. For subscribers lines having a length of 5 Km, such as occur in the telephony network, this results in a bandwidth of approximately 140 MHz. A time-division-multiplex of more than two digital television-video signals therefore would not fit in this frequency band.